Enrique V. Ramos-Fernandez

Co@NH2-MIL-125(Ti): cobaloxime-derived metal–organic framework-based composite for light-driven H2 production

We present a synthetic strategy for the efficient encapsulation of a derivative of a well-defined cobaloxime proton reduction catalyst within a photoresponsive metal–organic framework (NH2-MIL-125(Ti)). The resulting hybrid system Co@MOF is demonstrated to be a robust heterogeneous composite material. Furthermore, Co@MOF is an efficient and fully recyclable noble metal-free catalyst system for light-driven hydrogen evolution from water under visible light illumination.

Interplay of metal node and amine functionality in NH2-MIL-53: modulating breathing behavior through intra-framework interactions.

A series of amino-functionalized MIL-53 with different metals as nodes has been synthesized. By determining adsorption properties and spectroscopic characterization, we unequivocally show that the interaction between the amines of the organic linker and bridging μ(2)-OH of the inorganic scaffold modulates metal organic framework (MOF) flexibility. The strength of the interaction has been found to correlate with the electropositivity of the metal.

From biodiesel and bioethanol to liquid hydrocarbon fuels: new hydrotreating and advanced microbial technologies

Biodiesel and bioethanol, produced by simple and well-known transesterification and fermentation technologies, dominate the current biofuel market. However, their implementation in the hydrocarbon-based transport infrastructure faces serious energy-density and compatibility issues. The transformation of biomass into liquid hydrocarbons chemically identical to those currently used in our vehicles can help to overcome these issues eliminating the need to accommodate new fuels and facilitating a smooth transition toward a low carbon transportation system. These strong incentives are favoring the onset of new technologies such as hydrotreating and advanced microbial synthesis which are designed to produce gasoline, diesel and jet fuels from classical biomass feedstocks such as vegetable oils and sugars. The present Perspective paper intends to provide a state-of-the-art overview of these promising routes.

Towards efficient polyoxometalate encapsulation in MIL-100(Cr): influence of synthesis conditions

The one-pot encapsulation of phosphotungstic acid in the metal–organic framework MIL-100(Cr) has been studied under different synthesis conditions. Both conventional and microwave heating methods have been explored for three different solvent systems: pure aqueous or organic (DMF) phase and biphasic mixtures (water/2-pentanol). Biphasic systems yielded crystals with similar textural properties as those formed in water. The use of DMF as solvent promotes the formation of gel-like solids with dual porosity and enhanced accessibility. The addition of phosphotungstic acid (PTA, H3PW12O40.xH2O) to the MIL-100(Cr) synthesis mixture results in its direct encapsulation. 31P MAS NMR, elemental analysis, N2 adsorption and FT-IR spectroscopy confirm the incorporation of PTA in the sample. The highest PTA encapsulation loading (30 wt%) was obtained by synthesis with microwave heating in biphasic solvent systems (W/Cr molar ratio range between 0.5 and 0.25). Microwave irradiation decreases the time of synthesis (from 4 days to 3 hours) while the use of biphasic media preserves the PTA integrity without affecting the formation of the MOF. The interaction of PTA with the MIL-100(Cr) structure results in some loss of the Lewis acidity, while the Bronsted acidity is hardly affected.

Chloromethylation as a functionalisation pathway for metal–organic frameworks

A mild and safe chloromethylation of metal–organic frameworks is presented. After this post-synthetic functionalization, chlorine can be substituted by a wide range of moieties to obtain various multifunctional materials. The method can in principle be extended to coordination polymers with exposed aromatic rings.

Titania-catalysed oxidative dehydrogenation of ethyl lactate: effective yet selective free-radical oxidation

We research here the catalytic oxidative dehydrogenation of ethyl lactate, as an alternative route to ethyl pyruvate. Testing various solid catalysts (Fe2O3, TiO2, V2O5/MgO–Al2O3, ZrO2, CeO2 and ZnO), we find that simple and inexpensive TiO2 efficiently catalyses this reaction under mild conditions. Furthermore, molecular oxygen was used as the terminal oxidant. Importantly, this reaction runs well also using inexpensive commercial solvent mixtures. Both the desired reaction and the by-products formation follow a free-radical mechanism. Remarkably, adding activated carbon, a solid radical scavenger, hardly affects the catalytic activity, but enhances the product selectivity. This is because this solid radical scavenger hampers the formation of undesired products in solution, without suppressing the oxidation at the catalyst surface.

Understanding the solar-driven reduction of CO2 on doped ceria

With the appropriate materials, one can construct redox cycles that use CO2 as the oxidant, generating CO as the product. Here, we investigate thermochemical cycles using doped ceria compounds as the oxygen exchange medium. Doped samples are prepared using La, Cr, W, Zr, V, Y, and Ti as dopants. Studying the redox kinetics, we show that doping the pure ceria with zirconium strongly increases overall CO production, albeit at lower reaction rates. This is because the CO2 reduction step is second-order with respect to Ce(III). Doping the fluorite lattice with zirconium cations decreases the number of Ce(III) ions at the surface, and consequently slows down the reaction. This result is counter-intuitive, since normally you would think that the more reduction, the better. But the reactivity towards CO2 is actually determined by the surface Ce(III) ions, and so migration of dopant ions on the surface reduces its reactivity, even though the bulk Ce(III) concentration is higher. Our results demonstrate the importance of understanding surface kinetics when designing oxygen exchange materials for solar reactors.

Synthesis, characterization and testing of a new V2O5/Al2O3–MgO catalyst for butane dehydrogenation and limonene oxidation

We report the synthesis and characterization of new V2O5/Al2O3-MgO catalysts and their application in oxidative dehydrogenation and epoxidation reactions. The materials were prepared by wet impregnation under excess acid conditions. Anchoring of the desired species on the support occurs via an exchange reaction between the vanadium complex and surface hydroxyl groups. The IR and UV-Vis spectra of these catalysts indicate the presence of monomeric vanadium species at 5 wt% V2O5 loading, along with small amounts of polymeric species at 5 and 10 wt% V2O5 loadings. Electron paramagnetic resonance (EPR) spectroscopy reveals the presence of ferromagnetic VO(2+) dimers following calcination at 773 K. The catalysts were then tested in two reactions, namely the gas phase oxidative dehydrogenation of n-butane under flow conditions at 773 K and the liquid phase epoxidation of limonene with H2O2. The dehydrogenation reaction gave butenes and 1,3-butadiene in moderate selectivity at 8-10% conversion. The epoxidation of limonene was less successful, giving 50-70% selectivity to the 1,2-epoxide at 10-20% conversion.

Influence of the Oxidation Process of Carbon Material on the Mechanical Properties of Cement Mortars

The present research investigates how the addition of processed carbon materials affects the mechanical properties of cement mortars. Five types of oxidation treatments (air at 250°C, air at 410°C, ozone, H2O2, and HNO3) were applied to graphite powder, powdered carbon fiber, and short carbon fiber to assess the influence of the modification of the carbon material surface in the interaction between cement paste and carbon material. The best oxidation treatment in terms of mechanical strength improvement was oxidation by air at 410°C because this procedure yielded the highest amount of oxygen surface functional groups, thus producing a better interaction with cement paste. Ozone treatment has also been shown to produce a high level of improvement in mechanical properties, but in this case the properties are improved because of the rough surface of the carbon materials.

Induced Chirality in a Metal–Organic Framework by Postsynthetic Modification for Highly Selective Asymmetric Aldol Reactions

A straightforward synthetic route to chiral metal–organic frameworks is proposed that relies on an acid–base interaction between an acid linker and a chiral primary amino acid derived diamine organocatalyst. High ee values for the aldol condensation of linear ketones and aromatic aldehydes are reported with this heterogeneous catalyst. Three consecutive catalyst reuse experiments demonstrated that the majority of the activity was preserved, as was the enantioselectivity.